This invention relates to a rubber crawler comprising an endless rubber belt directed around two toothed wheels, whereby in circumferential direction of the belt parallel metal core elements are embedded in the rubber belt and extend in cross direction of the rubber belt and are provided for guiding supporting rolls provided between said wheels.
From EP-A-30.488 a rubber crawler is known which is driven around a toothed sprocket wheel and intermediate wheel. In the interior of the rubber crawler, distributed over the internal circumference of the belt, between the sprocket wheel and intermediate wheel, supporting rolls are provided for supporting the rubber belt. In longitudinal direction of the belt, at a regular distance from each other, metal core elements are partly embedded in the rubber, at a regular distance from each other. Each metal core element contains a basis with two wings that extend in transversal direction of the belt. The basis is provided with a guiding which forms the running surface for the supporting rolls. Between the guidings of successive core elements, a rubber layer of rubber of the belt is present. In the middle of the rubber crawler, between successive metal core elements, sprocket holes are provided for receiving teeth of the sprocket wheel for driving the rubber belt.
During the displacement of the rubber crawler over the bottom, the supporting rolls roll over the guidings of successive metal core elements and the intermediate rubber. Because the running surface of the supporting rolls is discontinuous, the displacement of the supporting rolls mostly involves an undesired raising and downward movement of the supporting rolls. This raising and downward movement of the supporting rolls involves undesired vibrations in the rubber crawler and an undesired noise pollution.
The rubber crawler disclosed in EP-A-300.488 contains in the middle part two projections extending in the direction of the interior of the rubber belt. To decrease the above described vibrations and damaging of the beltxe2x80x94due to the deposition of water, sand etc. between the contact surface of the rubber with the metal core elements through defects in the surface of the rubber beltxe2x80x94the basis of the metal core elements facing the interior of the rubber belt is provided with an extension. This extension is situated between each projection and an end of the metal core element, extends in longitudinal direction of the belt and constitutes the running surface of the supporting rolls.
The rubber crawler known from EP-A-300.488 however presents the disadvantage that the vibrations caused by the rolling of the supporting rolls over the metal core elements, are still too large. Upon displacement of the machine over transverse obstructions and the rotation of the rubber belt around its transversal axis when taking a bend, the metal core elements are moreover subjected to relatively large forces. This involves a regular breaking of the metal core elements out of the rubber belt. This is undesired.
It is the aim of the present invention to provide a rubber crawler wherein the above described vibrations following the displacement of the supporting rolls over the metal core elements can be further decreased.
This is achieved with this invention in that each metal core element comprises a guiding for guiding the supporting rolls and a carrier for receiving the guiding. The carrier and guiding are executed as separate parts and are connected with each other.
Due to the separation of the metal core element in at least two separate parts, that are dissociated from each other, namely a first part containing the guiding for the supporting rolls and a second part containing a carrier for this guiding, the forces exerted by the supporting rolls to the guiding are decomposed into components. This decomposition of the forces provides the possibility of reducing the net forces that are transferred from the guiding, through the connection to the carrier. As a consequence, also the forces that act upon the contact surface of the carrier with the rubber belt, can be reduced so that the metal core elements will less easily break out of the rubber. The splitting of the metal core element in a guiding and a carrier for this guiding thus allows to reduce the forces that act upon the contact surface of the metal core element with the surrounding rubber belt, and that are responsible for the destruction of the bond of the metal core element in the rubber belt and the breaking out of the metal core elements from the rubber belt.
A man skilled in the art would never consider to produce a metal core element for a rubber crawler out of several parts. A man skilled in the art will usually assume that a rigid support for a rubber belt, which must be capable of absorbing rather high traction and torsion forces, and of distributing these forces more or less uniform over the rubber belt, should be a massive entity. The man skilled in the art will rather assume that by the splitting of the metal core element in two or more parts, the strength of the metal core element is broken and as a consequence, the strength of the rubber crawler will be adversely influenced. In addition to this, by the splitting of the metal core element in a guiding and a carrier for the guiding, a part with a smaller mass must ensure the absorption and distribution of the forces over the rubber. The man skilled in the art will thereby assume that by the smaller mass of the carrying part, the forces to which the metal core elements are subjected, will be capable of overcoming the bonding of the core element in the rubber and that thus the breaking of the metal core elements out of the rubber belt is facilitated. It appears that this is not the case.
The guiding of the metal core element of this invention can be made as one entity or in two separate parts.
Between the guiding and the carrier, preferably a damping layer is provided, for at least partly absorbing and reducing the vibrations that are amongst others caused by the displacement of the supporting rolls over the guiding. Because these vibrations can at least partly be neutralised by the damping layer, the forces that must be transferred from the guiding to the carrier, can be correspondingly decreased. In that way the possibility of the core elements to break out of the rubber belt can be further decreased. The damping layer ensures simultaneously that the noise pollution caused by the displacement of the supporting rolls over the metal core elements can be decreased and prevents that vibrations originating from the outside can be transferred simply towards the inside of the rubber crawler.
In order to facilitate the displacement over transversal obstacles and to allow thereby that the rubber crawler thereby adapts itself to the obstacle, and in order to prevent that vibrations of the supporting rolls during their displacement over successive guidings are adversely increased, the guiding is preferable tiltably mounted in the carrier. This allows the guiding to position itself independently of the carrier, that the continuity of the running surface of the supporting rolls to be adversely affected to a lesser extent. The tiltable mounting namely allows that the guiding of a metal core element upon overcoming an obstacle can tilt somewhat in the direction of the guiding of a subsequent core element, so that the level difference that must be overcome by the supporting rolls during their displacement over successive guidings can be reduced and the associated vibrations can be correspondingly reduced.
The metal core element of the rubber crawler of this invention preferably comprises means for mechanically anchoring the metal core elements in the rubber belt.
An analysis of the driving of the rubber crawler namely has shown that during the driving, the sprocket wheel and intermediate wheel engage the sprocket holes and that thereby relatively high traction forces are exerted to the edges of the sprocket holes. These traction forces are transferred to the metal core elements and therefrom to a steel cord applied in longitudinal direction of the rubber crawler. In the known rubber crawler, the surface of the metal core element is subjected to a chemical treatment to establish a bonding of the metal to the rubber, and to allow a good transmission of traction forces from the metal core element is to the rubber. The thus obtained bonding is however insufficient. It has namely been shown that the metal is loosened from the rubber and the metal core elements can break out of the rubber belt when a massive obstacle, for example a piece of stone or a rock becomes clamped between the supporting rolls and the rubber belt. By providing a mechanical anchoring of the metal core elements, besides a chemical bonding, an improved anchoring of the metal core elements can be obtained, and it becomes possible to avoid that the metal core elements break out of the rubber crawler.
In a preferred embodiment of this invention, the carrier comprises in transversal direction of the rubber belt, a first and a second hole extending in height direction of the carrier, and the guiding comprises a first and a second protrusion. The first and second protrusion are provided to extend throughout respectively the first and second hole, so as to provide a simultaneous anchoring of the guiding and the carrier.
The first and second protrusion preferably comprise a hole that extends in longitudinal direction of the belt, for receiving a steel cord extending in longitudinal direction of the belt. The steel cord is provided for extending through holes in successive guidings. In the known rubber crawler mostly one or more parallel extending steel cords are provided in circumferential direction of the rubber crawler as reinforcing material for absorbing traction forces arising during the displacement of the rubber crawler. In this preferred embodiment, the steel cord fulfils a double function and functions also as a means for anchoring the metal core element in the rubber crawler.
In order to avoid that the steel cord be subjected to too much wearing, following friction between the steel cord and the mechanical anchoring, means for protecting the steel cord can be provided. This can for example be realised by providing the interior of the holes described above, with a protective rubber layer, by embedding the steel cord in protective rubber, by providing a double row of steel cord, so that the steel cord extends throughout almost the whole hole, or to provide in the hole a metal plate that extends in longitudinal direction of the belt. Also other means known to the man skilled in the art for decreasing the friction arising between the steel cord and the mechanic anchoring means, can be used.
The carrier and guiding are further preferably provided with co-operating, complementary surfaces, so as to allow an improved position of the guiding and carrier with respect to each other.
The carrier and guiding can be made of the same or different materials. By the separation of the carrier which mainly has a carrying function, from the guiding which mainly has a transport function, each of these parts can be made in the material that is optimally adapted to its function. The carrier is preferably made of a material with a high toughness and is capable of absorbing the forces exerted tot he guiding and distributing them in an optimum way and transferring them to the rubber belt. The guiding is preferably made of a material with a good wearing resistance, so as to retard wearing of the guiding surfaces.
The present invention also relates to a metal core element as part of the above described rubber crawler.